The present invention relates to a heat transfer image-receiving or imageable sheet and, more particularly, to a heat transfer imageable sheet having improved releasability at the time of heat transfer.
Heretofore, various heat transfer techniques have been known in the art, including sublimation type transfer systems wherein a sublimable dye as a recording material is carried on a substrate sheet such as paper or a plastic film to make a heat transfer sheet, which is in turn overlaid on paper or a plastic film containing a dye-receiving layer to make various full-color images thereon.
In such systems, thermal heads of printers are used as heating means to transfer three-, four-, or more-colored dots to heat transfer image-receiving sheets, thereby reproducing full-color images of manuscripts with the multicolor dots.
According to the above heat transfer systems, imaging is achieved by overlaying a dye layer of a heat transfer sheet on a dye-receiving layer of a heat transfer image-receiving sheet so as to oppose each other and heating them by a thermal head to transfer a dye to the dye-receiving layer, and the dye and dye-receiving layers are both formed of thermoplastic resin. Thus, problems with these systems are that the two layers are so fused together at the time of heat transfer that difficulty is encountered in their separation, causing damage to the resulting image.
In order to provide a solution to such problems, it has been proposed to add a release agent to the dye-receiving layer and to bleed it out onto the surface of the dye-receiving layer to form a release layer.
When a liquid or waxy release agent is used to this end, it is likely to contaminate other articles or cause discoloration, etc. of images. As an alternative, it has thus been proposed to use a reactive curing type of release agent.
With this release agent, the problems as referred to above are solved to some extent as a result that after the formation of a dye-receiving layer, heating is carried out to bleed out the release agent contained in the dye-receiving layer onto its surface, whereby a thin, crosslinked film of the release agent is formed on the surface of the dye-receiving layer. However, when there is a certain interval of time between forming the dye-receiving layer and forming the release layer for reasons of production process, for instance, when the two layers are formed with separate equipment in separate spots, the reactive curing type of release agent in the dye-receiving layer undergoes gradual reaction and curing, without bleeding of the release agent, in the meantime. For this reason, there arises a problem that even when heat treatment is thereafter applied to form the release layer, any release layer of sufficient releasability cannot be obtained at all.
It is, therefore, a primary object of the present invention to provide a heat transfer image-receiving sheet having improved releasability, and which is retained with no drop even when there is a certain interval of time between forming a dye-receiving layer and forming a release layer.